Information processing apparatus and method

ABSTRACT

To limit use of content, when a source receives a request for transmitting content from a sink, the source performs an authentication process. When the authentication is successful, the source transmits to the sink key information necessary for decrypting the encryption applied to the content. The sink can receive the content by receiving the key information and by decrypting the encryption applied to the content by using the key information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/770,002, filed on Feb. 19, 2013, which is a continuation of U.S.application Ser. No. 12/842,312, filed on Jul. 23, 2010, which is acontinuation of U.S. application Ser. No. 12/002,805, filed on Dec. 19,2007, now U.S. Pat. No. 7,779,260, which is a continuation of U.S.application Ser. No. 09/900,584, filed on Jul. 6, 2001, now U.S. Pat.No. 7,343,491, which claims priority from Japanese Application Nos.P2000-205615, filed Jul. 6, 2000, and P2000-211787, filed Jul. 12, 2000,the disclosures of which are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to an information processing apparatus andmethod. More particularly, the present invention relates to aninformation processing apparatus and method in which use of content canbe limited.

In recent years, network systems typified by the Internet have becomepopular. As a result, it is now possible for users to transmit orreceive information via the Internet.

A user who wants to view or listen to authored material such as moviesor music can pay to receive the authored material.

However, there is a risk that in addition to the owner, other people,who have not paid to receive authored material such as movies or music,may fraudulently view or listen to the authored material through anetwork such as the Internet.

Also, if illegal viewing or listening through a network continuesunrestrained, the content creation and distribution business willsuffer.

SUMMARY OF THE INVENTION

The present invention has been made in view of such circumstances. Anobject of the present invention is to prevent content from beingillegally used via a network.

To this end, in one aspect, the present invention provides aninformation processing apparatus for transmitting content to anotherapparatus via a network. The information processing apparatus includesan encryption unit operable to encrypt the content; an authenticationunit operable to perform an authentication procedure with the anotherapparatus when the another apparatus requests permission to receive theencrypted content, the authentication procedure providing anauthentication result; a transmitter operable to transmit a decryptionkey for decrypting the encrypted content to the another apparatus basedon the authentication result; a first obtaining unit operable to obtainidentification information of the another apparatus based on theauthentication result; a first counting unit operable to count a totalnumber of units desiring to receive the encrypted content based on theidentification information; a storage unit operable to store theidentification information of the another apparatus; and a controlleroperable to control a total number of units approved to receive theencrypted content based on the total number of units desiring to receivethe encrypted content.

The information processing apparatus may further include a secondobtaining unit operable to obtain a number of additional units desiringto receive the encrypted content from the another apparatus based on theauthentication result; and a second counting unit operable to count atotal number of units of the another apparatus desiring to receive theencrypted content based on the number of additional units.

The information processing apparatus may further include an informationupdating unit operable to delete the identification information storedin the storage unit and to reset the total number of units approved toreceive the encrypted content when the decryption key is changed.

In another aspect, the present invention provides a method fortransmitting content from an information processing apparatus to anotherapparatus via a network. The method includes encrypting the content;performing an authentication procedure with the another apparatus whenthe another apparatus requests permission to receive the encryptedcontent, the authentication procedure producing an authenticationresult; transmitting a decryption key for decrypting the encryptedcontent to the another apparatus based on the authentication result;obtaining identification information of the another apparatus based onthe authentication result; counting a total number of units desiring toreceive the encrypted content based on the identification information;storing the identification information of the another apparatus; andcontrolling a total number of units approved to receive the encryptedcontent based on the total number of units desiring to receive theencrypted content.

In another aspect, the present invention provides a recording mediumhaving recorded thereon a program for transmitting content from aninformation processing apparatus to another apparatus in a network, theprogram including encrypting the content; performing an authenticationprocedure with the another apparatus when the another apparatus requestspermission to receive the encrypted content, the authenticationprocedure producing an authentication result; transmitting a decryptionkey for decrypting the encrypted content to the another apparatus basedon the authentication result; obtaining identification information ofthe another apparatus based on the authentication result; counting atotal number of units desiring to receive the encrypted content based onthe identification information; storing the identification informationof the another apparatus; and controlling a total number of unitsapproved to receive the encrypted content based on the total number ofunits desiring to receive the encrypted content.

In the information processing apparatus, the information processingmethod, and the program recorded on the recording medium, content isencrypted, and when a request for reception permission is made fromanother apparatus, an authentication procedure is performed with theother apparatus as long as the number of receiving units does not exceeda permissible value even if the reception is permitted, and a decryptionkey for decrypting the encrypted content is transmitted to the otherapparatus on the basis of the authentication result.

In another aspect, the present invention provides an informationprocessing apparatus for receiving content from a first apparatus via afirst network. The information processing apparatus includes a firsttransmitter operable to transmit to the first apparatus a request forpermission to receive the content; a first authentication unit operableto perform a first authentication procedure with the first apparatus,the first authentication procedure producing a first authenticationresult; a receiver operable to receive from the first apparatus a firstdecryption key for decrypting the content based on the firstauthentication result; a second transmitter operable to transmit thecontent received from the first apparatus to a second apparatus via asecond network; a second authentication unit operable to perform asecond authentication procedure with the second apparatus when a requestfor permission to receive the content is made from the second apparatus,the second authentication procedure producing a second authenticationresult; a third transmitter operable to transmit a second decryption keyto the second apparatus based on the second authentication result; afirst obtaining unit operable to obtain identification information ofthe second apparatus based on the second authentication result; a firstcounting unit operable to count a number of units desiring to receivethe content based on the identification information; a storage unitoperable to store the identification information of the secondapparatus; and a controller operable to control a number of unitsapproved to receive the content based on the number of units desiring toreceive the content.

The information processing apparatus of the present invention mayfurther include a decryption unit operable to decrypt the content; andan encryption unit operable to encrypt the content decrypted by thedecryption unit.

The information processing apparatus of the present invention mayfurther include a fourth transmitter operable to transmit the number ofunits desiring to receive the content to the first apparatus based onthe first authentication result; a second obtaining unit operable toobtain a number of additional units desiring to receive the content fromthe second apparatus based on the second authentication result; and asecond counting unit operable to count a total number of units of thesecond apparatus desiring to receive the content based on the number ofadditional units.

The information processing apparatus in accordance with this aspect ofthe present invention may further include an information updating unitoperable to delete the identification information stored in the storageunit and to reset the number of units approved to receive the contentwhen the second decryption key is changed.

In another aspect, the present invention provides a method for receivingcontent in an information processing apparatus from a first apparatusvia a first network. The method includes transmitting to the firstapparatus a request for permission to receive the content; performing afirst authentication procedure with the first apparatus to obtain afirst authentication result; receiving from the first apparatus a firstdecryption key for decrypting the content based on the firstauthentication result; transmitting the content received from the firstapparatus to a second apparatus via a second network; performing asecond authentication procedure with the second apparatus when a requestfor permission to receive the content is made from the second apparatus,the second authentication procedure producing a second authenticationresult; transmitting a second decryption key to the second apparatusbased on the second authentication result; obtaining identificationinformation of the second apparatus based on the second authenticationresult; counting a number of units desiring to receive the content basedon the identification information; storing the identificationinformation of the second apparatus; and controlling a number of unitsapproved to receive the content based on the number of units desiring toreceive the content.

In another aspect, the present invention provides a recording mediumhaving recorded thereon a program for receiving content in aninformation processing apparatus from a first apparatus via a network.The program includes transmitting to the first apparatus a request forpermission to receive the content; performing a first authenticationprocedure with the first apparatus to obtain a first authenticationresult; receiving from the first apparatus a first decryption key fordecrypting the content based on the first authentication result;transmitting the content received from the first apparatus to a secondapparatus via a second network; performing a second authenticationprocedure with the second apparatus when a request for permission toreceive the content is made from the second apparatus, the secondauthentication procedure producing a second authentication result;transmitting a second decryption key to the second apparatus based onthe second authentication result; obtaining identification informationof the second apparatus based on the second authentication result;counting a number of units desiring to receive the content based on theidentification information; storing the identification information ofthe second apparatus; and controlling a number of units approved toreceive the content based on the number of units desiring to receive thecontent.

In the information processing apparatus, the information processingmethod, and the program recorded on the recording medium, the contentreceived from the first apparatus via the first network is transmittedto the second apparatus via the second network with the permissiblenumber of units obtained from the first apparatus as an upper limit.

The above and further objects, aspects and novel features of theinvention will become more fully apparent from the following detaileddescription when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of the configuration of anetwork system to which the present invention is applied;

FIG. 2 is a block diagram showing a detailed example of the constructionof a source of FIG. 1;

FIG. 3 is a block diagram showing a detailed example of the constructionof a sink of FIG. 1;

FIG. 4 is a block diagram showing a detailed example of the constructionof a bridge of FIG. 1;

FIG. 5 is an illustration of an authentication process between a sourceor a bridge, and a sink;

FIG. 6 is a flowchart illustrating an authentication process by the sinkfor a source or a bridge;

FIG. 7 is a flowchart illustrating an authentication process by a sourceor a bridge for a source;

FIG. 8 is a flowchart illustrating an authentication process by a sourceor a Tx bridge for an Rx bridge;

FIG. 9 is a flowchart illustrating an authentication process by the Rxbridge for the source or the Tx bridge; and

FIG. 10 is a flowchart illustrating an authentication process by thesource or the Tx bridge for the Rx bridge.

DETAILED DESCRIPTION

FIG. 1 is a block diagram showing an example of the configuration of anetwork system to which the present invention is applied. In thisnetwork system, a source 1 is connected to a sink 2-1 and a bridge 3-1via a bus 4-1. The bridge 3-1 is connected to a sink 2-2 and a bridge3-2 via a bus 4-2. Furthermore, the bridge 3-2 is connected to sinks 2-3and 2-4 via a bus 4-3.

The source 1 is an output device for outputting content. When content isto be output, the source 1 encrypts the content, then outputs theencrypted content to the sinks 2-1 to 2-4 via the buses 4-1 to 4-3. Keyinformation necessary for decrypting the encrypted content istransferred only to the sink which has succeeded in an authenticationprocess. As a result, the number of sinks which receive the content islimited. Since the bridges 3-1 and 3-2 (to be described later) onlyre-output a received signal, these are excluded from the object forwhich the number of units is counted.

Sinks 2-1 to 2-4 (hereinafter, when the sinks 2-1 to 2-4 do not need beindividually identified, they are referred to simply as a “sink 2”, andthe same applies to other devices) are receiving units for receivingcontent supplied from the source 1. If a sink 2 succeeds in theauthentication process, the sink 2 decrypts the received content on thebasis of the key information transferred from the source 1. However,when the bridges 3-1 and 3-2 decrypt the encryption once, and encryptwith a new key and output the encrypted content, the sinks 2-2 to 2-4decrypt the received content on the basis of the key informationtransferred from the bridge which is connected directly thereto.

It is assumed that the bridges 3-1 and 3-2 receive and decrypt theencrypted content which is output from the source 1, re-encrypt thecontent, and then output it to the sinks 2-2 to 2-4. For this purpose,the bridge 3-1 performs an authentication process with the source 1,obtains key information necessary for decrypting the encrypted content,and tells the source 1 the number of sinks 2 for which the content to bere-output is desired to be received. Then, when the bridge 3-1 obtainspermission from the source 1, the bridge 3-1, instead of the source 1,limits the number of sinks 2-2 to 2-4 which receive the content. Thebridge 3-2 performs an authentication process with the bridge 3-1, andsimilarly limits the number of sinks 2-3 and 2-4 which receive thecontent.

FIG. 2 is a block diagram showing a detailed example of the constructionof the source 1.

When a medium 12 is loaded, a content player 11, under the control of acontrol section 15, plays back the content recorded on the medium 12,and outputs the content to an encryption section 13. The encryptionsection 13 encrypts the content input from the content player 11, andoutputs it externally via a communication interface (I/F) 14. In placeof the content player 11 and the medium 12, a source having a tunerwhich receives and outputs broadcast content may be used.

The control section 15 controls the content player 11, the encryptionsection 13, the communication I/F 14, and a storage section 16. Also,the control section 15 causes the content played back by the contentplayer 11 to be stored in the storage section 16 as necessary.

FIG. 3 is a block diagram showing a detailed example of the constructionof a sink 2.

A control section 24 controls an image/audio output section 21, adecryption section 22, a communication I/F 23, and a storage section 25.Also, the control section 24 sends the encrypted content, transmittedvia the communication I/F 23, to the decryption section 22.

The decryption section 22 obtains the key information transmitted fromthe source 1 through the communication I/F 23. Also, the decryptionsection 22 decrypts the content on the basis of the obtained keyinformation. The image/audio output section 21 outputs the contentdecrypted by the decryption section 22.

FIG. 4 is a block diagram showing a detailed example of the constructionof a bridge 3.

A control section 35 controls a communication I/F 31, a decryptionsection 32, an encryption section 33, a communication I/F 34, and astorage section 36. Also, the control section 35 sends the encryptedcontent, transmitted via the communication I/F 31, to the decryptionsection 32.

The decryption section 32 obtains the key information transmitted fromthe source 1 via the communication I/F 31, and decrypts the receivedcontent on the basis of the obtained key information.

The encryption section 33 encrypts the content decrypted by thedecryption section 32, and externally outputs it via the communicationI/F 34.

It is assumed that, for authentication, public-key cryptographictechnology is used, and that the source 1, the sink 2, and the bridge 3each have a digital certificate (hereinafter referred to as a“certificate”), issued by the key management organization, a secret key,and a public key of the key management organization. It is assumed thatthis certificate contains a public key for each device, corresponding tothe secret key for each device, the unique ID of each device, and anelectronic signature for these two pieces of data supplied by the keymanagement organization.

FIG. 5 is an illustration of an authentication process in a case wherethe source 1 and the sink 2-1 (FIG. 1) are directly connected.

Initially, the sink 2-1 transmits its own certificate to the source 1.Specifically, the control section 24 of the sink 2-1 reads a certificatefrom the storage section 25, and transmits it as a communication commandto the source 1 via the communication I/F 23 ({circle around (1)} inFIG. 5).

When the source 1 receives this communication command, the source 1determines whether or not the data is valid. Specifically, the controlsection 15 of the source 1 checks whether or not the data in thecertificate received via the communication I/F 12 corresponds to theelectronic signature of the key management organization attached theretoby using the public key of the key management organization stored in thestorage section 16. That is, the control section 15 determines thevalidity of the received data by performing a DSA (Digital SignatureAlgorithm) verification computation process for public key encryption.If the determination result shows that the received data is valid, theauthentication process continues. Otherwise, the authentication processis terminated.

If the processing continues, the control section 15 of the source 1checks whether or not the ID of the other party in the certificate hasalready been entered in the authenticated ID list (hereinafter describedas an “ID list”) stored in the storage section 16. If the certificatehas already been entered, “0” is substituted in a variable CntUp.

If, on the other hand, the ID of the other party in the certificate hasnot been entered in the ID list, the control section 15 of the source 1compares the number of sinks 2 for which reception has been permitted(hereinafter described as a “variable SinkCnt”) with the upper-limitnumber which indicates the number of receptions which are permitted(hereinafter described as a “variable MaxSink”). When the variableSinkCnt is smaller, “1” is substituted in the variable CntUp.

When SinkCnt=MaxSink, the authentication process is terminated. Also,the variable MaxSink may not be a variable (that is, it may be aconstant).

Then, the control section 15 of the source 1 generates a pseudo-randomnumber Random_challenge on the basis of a pseudo-random numbergeneration algorithm, and transmits it as a communication command to thesink 2 ({circle around (2)} in FIG. 5).

When the control section 24 of the sink 2-1 receives this communicationcommand, the control section 24 performs a DSA Sign computation processfor public key encryption on the value thereof by using its own secretkey stored in the storage section 25 in order to calculate theelectronic signature. The control section 24 of the sink 2-1 transmitsthe calculated electronic signature, as a communication command(Response data), to the source 1 ({circle around (3)} in FIG. 5).

When the control section 15 of the source 1 receives this communicationcommand, the control section 15 determines whether or not thepseudo-random number Random challenge transmitted by the control section15 corresponds to this electronic signature, that is, performs theabove-mentioned DSA verification computation process in order todetermine the validity of the data. Here, however, in place of theabove-described public key of the key management organization, thepublic key of the other party in the certificate received from the otherparty is used. When the result of the determination shows that the datais valid, the authentication process is continued. Otherwise, theauthentication process is terminated.

When the processing continues, the control section 15 of the source 1transmits to the sink 2-1, as a communication command, key informationnecessary for decrypting the encryption applied to the content ({circlearound (1)} in FIG. 5), and increases the value of the variable SinkCntby the value of the variable CntUp. Then, the control section 15 of thesource 1 checks whether or not the ID of the other party in thecertificate has already been entered in the authenticated ID list storedin the storage section 16. If it has already been entered, “0” issubstituted in the variable CntUp. On the other hand, if the ID of theother party in the certificate has not been entered in the ID list, thevariable SinkCnt is compared with the variable MaxSink, and if thevariable SinkCnt is smaller, “1” is substituted in the variable CntUp.

The sink 2-1 can receive the content by receiving the key informationand by decrypting the encryption applied to the content by using the keyinformation.

Also, as in the source 1 and the sink 2-2 shown in FIG. 1, in a casewhere the content output from the source 1 is received by the sink 2-2after going through the bridge 3-1, the sink 2-2 and the bridge 3-1perform an authentication process such as that shown in FIG. 5. That is,even in a case where content is transmitted via two or more bridges asin the source 1 and the sink 2-3 or the source 1 and the sink 2-4, thesource 1 and the last bridge 3-2 (the bridge which is directly connectedto the sinks 2-3 and 2-4) perform similar authentication processes.

The processing flow of the sink 2 in the above authentication process isshown in FIG. 6, and the processing flow of the source 1 is shown inFIG. 7.

The authentication process of the source 1 is the same as that of thecase of a sink 2 even if the other party is a bridge 3. For theauthentication process of the bridge 3, the process shown in step S15 ofFIG. 7 differs from that in the case of the sink 2. Specifically, whenSinkCnt=MaxSink, in order to increase the value of the variable MaxSink,the bridge 3 performs an authentication process for requesting receptionpermission from the source 1 or a bridge 3 (in the case of the exampleof FIG. 1, the source 1 if the bridge 3 is the bridge 3-1 and the bridge3-1 if the bridge 3 is the bridge 3-2) which is the transmission sourceof the content received (input) by the bridge 3. In this case, a requestfor an additional increase in the number of receiving units by one ormore is made. When this authentication process is successful, theprocessing of step S16 or subsequent steps in FIG. 7 is continued.

FIG. 8 is an illustration of an authentication process in a case wherethe source 1 and the bridge 3-1 (FIG. 1) are directly connected.

Initially, the control section 35 of the bridge 3-1 transmits its owncertificate, variable RelCnt, and variable AbsCnt to the source 1({circle around (1)} in FIG. 8). Here, the variable RelCnt representsthe number of units for which the bridge 3-1 desires to newly obtainreception permission, and the variable AbsCnt represents the totalnumber of units for which permission has already been obtained and thenumber of units for which permission is desired this time.

When the control section 15 of the source 1 receives the certificate andthe variables, the control section 15 determines whether or not thecertificate is valid by performing the above-described DSA verificationcomputation process. When the result of the determination shows that thecertificate is not valid, the authentication process is terminated.

When the processing continues, the control section 15 of the source 1checks whether or not the ID of the other party in the certificate hasalready been entered in its own ID list. If the certificate has alreadybeen entered, the variable RelCnt is substituted in the variable CntUp.

If, on the other hand, the ID of the other party in the certificate hasnot been entered in the ID list, the control section 15 of the source 1substitutes the variable AbsCnt in the variable CntUp. Then, the controlsection 15 of the source 1 determines whether the value resulting whenthe variable CntUp is added to the variable SinkCnt is smaller than thevariable MaxSink. When they are equal, the authentication process isterminated.

Then, the control section 15 of the source 1 generates a pseudo-randomnumber Random_challenge, and transmits it as a communication command tothe bridge 3-1 ({circle around (2)} in FIG. 8).

When the control section 35 of the bridge 3-1 receives thiscommunication command, the control section 35 performs theabove-described DSA Sign computation process on that value, and thetransmitted variable RelCnt and variable AbsCnt by using its own secretkey stored in the storage section 36 in order to calculate theelectronic signature. The control section 35 of the bridge 3-1 transmitsthe calculated electronic signature as a communication command (Responsedata) to the source 1 ({circle around (3)} in FIG. 8).

When the control section 15 of the source 1 receives this communicationcommand, the control section 15 determines whether or not thiselectronic signature corresponds to the pseudo-random numberRandom_challenge transmitted by the control section 15 and the receivedvariable RelCnt and variable AbsCnt, that is, determines the validity ofthe data by performing the DSA verification computation process. Here,however, in place of the above-described public key of the keymanagement organization, the public key of the other party in thecertificate received from the other party is used. When the result ofthe determination shows that the data is not valid, the authenticationprocess is terminated.

When the processing continues, the control section 15 of the source 1transmits, as a communication command, to the bridge 3-1 the keyinformation necessary for decrypting the encryption applied to thecontent ({circle around (4)} in FIG. 8), and increases the value of thevariable SinkCnt by the value of the variable CntUp. After this, if theID of the other party has not been entered in the ID list, the controlsection 15 adds it to the list.

The bridge 3-1 receives the key information and decrypts the encryptionapplied to the content by using the key information, re-encrypts thecontent, and then outputs it. Then, the control section 35 of the bridge3-1 increases the value of the variable MaxSink by the value of thevariable RelCnt.

The processing flow of the bridge 3 in the above authentication processis shown in FIG. 9, and the processing flow of the source 1 is shown inFIG. 10.

As in the source 1 and the sink 2-3 or the source 1 and the sink 2-4shown in FIG. 1, in a case where the content which is output from thesource 1 is received by the sinks 2-3 and 2-4 after going through two ofbridges 3-1 and 3-2 or more, the bridge 3-1 which outputs the content(hereinafter described as a “Tx bridge”) and the bridge 3-2 whichreceives it (hereinafter described as an “Rx bridge”) perform anauthentication process such as that shown in FIG. 8.

The authentication process of the Rx bridge is the same as that in thecase where the other party is the source 1.

For the authentication process of the Tx bridge, the process shown instep S46 of FIG. 10 differs from that of the case of the source 1.Specifically, when SinkCnt+CntUp>MaxSink, in order to increase the valueof the variable MaxSink, the Tx bridge performs an authenticationprocess for requesting the source 1 or the bridge 3, which is thetransmission source of the content input to the Tx bridge, to permitreception (in the case of the example of FIG. 1, the bridge 3-1 requestsauthentication from the source 1). In this case, a request foradditional information in the number of receiving units of((SinkCnt+CntUp)−MaxSink) or more is made. When this authenticationprocess is successful, the processing of step S50 and subsequent stepsof FIG. 10 continues.

As another processing example, a case in which the variable RelCnt andthe variable AbsCnt are transmitted separately from the certificate ispossible. For example, there is also a method of transmitting themtogether with the Response shown at {circle around (3)} in FIG. 8 ortransmitting them by a completely different communication command.

Also, there is a method in which in step S15 of FIG. 7 or in step S46 ofFIG. 10, when the bridges 3-1 and 3-2 perform an authentication processwith a newly connected source 1 or bridge 3, regardless of the result,the processing thereafter is not continued. That is, a newauthentication can be considered to be one for making subsequentauthentications successful.

Furthermore, in a case where the sink 2 stops receiving its own outputand loses information necessary for decrypting the encryption, thesource 1 or the bridge 3 can decrease the number of the variable SinkCntby the number corresponding to the number of sinks 2. For example, whenthe source 1 or the bridge 3 changes the key information for theencryption to be applied to the content, it is possible for the sink 2to set the variable SinkCnt to 0.

As described above, since the source 1 or the bridge 3 limits the numberof receiving units or sinks 2 capable of receiving output, theadvantages such as those described below are obtained.

-   -   (1) It is possible for the owner of content to prevent illegal        viewing and recording of the content.    -   (2) Even when a signal is re-output using a bridge, it is        possible for the source to limit the number of units, including        the sink which exists at the end of the bridge.    -   (3) Since the limitation of the number of units is performed        using an ID unique to the device, even if the same sink performs        authentication many times, the number of units will not be        increased by mistake.    -   (4) Since the increase or decrease in the number of receiving        units and the total number of receiving units are informed when        the bridge requests reception permission from the source or        another bridge, it is possible for the source and the other        bridge to easily change the variable SinkCnt to a correct value        in either the case where authentication with the bridge has been        performed or the case where authentication with the bridge has        not been performed.

Since public-key cryptographic technology is used, the device-unique IDand the requested number of units can be safely transferred to anotherunit, and correct number-of-devices management can be performed.

Although the above-described series of processes can be performed byhardware, these can also be performed by software. In the case where theseries of processes is performed by software, programs which form thesoftware are installed from a recording medium into a computerincorporated into dedicated hardware or, for example, into ageneral-purpose personal computer capable of executing various types offunctions by installing various programs.

This recording medium is constructed by not only packaged media formedof a magnetic disk (including a floppy disk), an optical disk (includinga CD-ROM (Compact Disk-Read Only Memory), and a DVD (Digital VersatileDisk)), a magneto-optical disk (including an MD (Mini-Disk)), or asemiconductor memory, in which programs are recorded, but also isconstructed by a ROM, a hard disk, etc., in which programs are stored,which is provided to a user in such a manner as to be preinstalled intoa computer.

In this specification, steps which describe a program stored in arecording medium contain not only processing performed in a time-seriesmanner along the described sequence, but also processing performed inparallel or individually although the processing is not necessarilyperformed in a time-series manner.

In this specification, the system represents the overall apparatuscomposed of plural devices.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A communication device that transmitsencrypted content, the communication device comprising: circuitryconfigured to transmit a random value to another communication device,to receive information that is generated by the another communicationdevice based on the random value and on a secret key stored in theanother communication device, and to judge whether the receivedinformation is mismatched with information held in the communicationdevice, wherein authentication of the another communication device isconsidered to have failed if the received information is mismatched withthe information held in the communication device, wherein the circuitrytransmits the random value as part of an initiation message transmittedto the another communication device, wherein the circuitry judgeswhether the received information is mismatched with the information heldin the communication device which is generated using the random value,wherein in response to the circuitry judging that the receivedinformation matches the information held in the communication device,the circuitry transmits key information to the another communicationdevice, wherein the circuitry updates a count of other communicationdevices that receive the key information based on whether the anothercommunication device is currently registered in a registration list,wherein the response to the circuitry determining that the anothercommunication device is not registered in the registration list, thecircuitry updates the count by adding an additional value to the count,wherein the response to the count being equal to the predefined ,maximumvalue and the another communication device not being already registeredin the registration list, an authentication is considered to havefailed, and wherein the circuitry deletes all other communicationdevices registered in the registration list and resets to zero the countof other communication devices that receive the key information inresponse to the key information being changed.
 2. The communicationdevice according to claim 1, wherein the key information permits theanother communication device to decrypt encrypted content transmitted bythe communication device.
 3. The communication device according to claim1, further comprising a communication interface (I/F), wherein thecircuitry transmits the random value to the another communication devicevia the communication interface, and receives the information generatedby the another communication device via the communication interface. 4.The communication device according to claim 1, further comprising: atuner configured to receive content.
 5. The communication deviceaccording to claim 4, wherein the circuitry is further configured toencrypt the received content using the key information and to transmitthe encrypted content to the another communication device if thereceived information matches the information held in the communicationdevice.
 6. The communication device according to claim 5, furthercomprising: a content player configured to play back content recorded ona recording medium.
 7. The communication device according to claim6,wherein the circuitry is further configured to encrypt the played backcontent using the key information and to transmit the encrypted contentto the another communication device if the received information matchesthe information held in the communication device.